1. Field
The present invention relates to ultra-wideband (UWB) directional circular-field-polarization antennae and can be used to receive/transmit UWB ultra-short pulses and narrow-band carrier-frequency-tunable signals.
2. Description of the Prior Art
UWB circular-field-polarization antennae are actively used in fixed communication systems if data transmission to an end user is necessary with the proviso that a user's antenna polarization is unknown. Examples of such devices can be communication devices arranged in the vicinity of a human body (BAN standard). A flat spiral antenna is a known type of UWB radiators that use the principles of self-complementarity and electrodynamic self-similarity. Slot and microstrip spiral antennae are widely used in various systems. To make a radiation of such antennae unidirectional, reflecting surfaces or absorbers arranged on one side of a spiral are used. Said techniques essentially deteriorate the antenna broadbandness and efficiency.
Strip “patch” (metal plate) cavities (multilevel strip cavities) coupled with a feed line by means of a slot aperture and used as UWB signal radiators are widely covered in the literature. Using non-resonant apertures for a beam pattern, similar systems can provide the property of unidirectionality. In such a case, however, the difficulty emerges with the requirement of radiating a circular-polarized signal, said difficulty resulting from the spiral antenna structure.
Known from US 2012229363 is a directional wideband antenna designed to enhance cell coverage within a building and comprising a spiral antenna with feed-point configured to transfer energy to/from the antenna, an energy absorbent backing to reduce a back lobe, a cavity behind the log-spiral slot antenna and in front of the energy absorbent backing, and a cable connector coupled to a shaped microstrip line coupled to the feed-point and designed to transform the input impedance to the antenna impedance. The disadvantage of the present solution is high loss caused by the absorbent, while said loss could be reduced at use of stacked strip cavities that however complicate the antenna structure.
Known from U.S. Pat. No. 7,106,255 B2 is an antenna that comprises a first patch including at least one slot-like part thereon, a second patch including at least one strip-like part thereon, wherein said slot-like parts at least partially cross each other thereby forming a coupling region. The disadvantage of such the antenna is that its gain factor is insufficient to implement communications for long distances. In addition, the present antenna has no circular polarization, and this absence may cause deterioration of the communication stability at variation of a mutual position of the receiving and transmitting devices; said absence does not allow use of the present antenna for communications between stationary and portable mobile devices.
The antenna disclosed in US 20040119642 A1 is designed for transmitting and receiving circularly polarized signals and uses strip elements of a special shape. Assigned to the disadvantages of said antenna should be that its gain coefficient is insufficient for said applications.